1. Field of the Invention
This invention relates to a method of making terminal nut for ignition plug by plastic working.
2. Description of the Prior Art
In an ignition plug in use for an internal combustion engine, there is provided a housing which includes an outer shell to facilitate mounting a plug body on a cylinder head. The housing encloses an insulator made from high purity alumina porcelain, for example, and an center and ground electrode to cause a discharge therebetween.
A terminal nut is capped on the top of the plug body to connect a high voltage cord to the center electrode.
This kind of the terminal nut has been usually made by cutting a metallic blank, otherwise by molding soft metals such as zinc and aluminium-based alloy by means of die casting.
The cutting method, however, produces waste chips, the quantity of which reaches as far as one-half volume of whole the blank so as to result in loss of material.
Further, the cutting method is time-consuming to reduce productivity. The die casting method invariably accompanies with dust, high temperature, considerable level of noise, and toxic gas by subjecting mold-removing agent to heated mold blocks. Thus presenting an adverse working condition, and having a risk to harmfully influence on health.
In addition, material of the blank available to the die casting method, is generally confined to only parts of soft metals such as zinc and aluminium-based alloy. Selection range of the blank materials is limited, and making it difficult to obtain sufficient hardness as a final product.
Therefore, it is an object of this invention to provide a method of making terminal nut which is capable of reducing a time required to be manufactured for an improved productivity with less cost.
According to this invention, there is provided a method of making a terminal nut comprising; first step in which a column-shaped metallic blank is set into a cylindrical die, and struck at both end surfaces to flatten the end surfaces in perpendicular to axial direction of said blank by means of plungers; second step in which a punching rod is forcibly caved into one end surface of said blank with other end surface of said blank supported by a conical headed mandrel to form a central conical dent at one end surface of said blank, and at the same time, forming first bottom-ended hole at other end surface of said blank; third step in which a punch rod is forcibly caved into said first bottom-ended hole to form second bottom-ended hole at said blank by means of reducing concentrically and continuously from said first bottom-ended hole to be diametrically lesser than said first bottom-ended hole; fourth step in which said blank is enclosed into a cylindrical die having a constricted inner wall to be axially contracted to bulge a side surface of said blank diametrically outward by means of upsetting; fifth step in which a perforation hole is axially formed at said blank by punching in concentrical relationship with said first bottom-ended hole, said perforation hole being diametrically corresponding to said second bottom-ended hole; sixth step in which said blank is shaved at its bulged portion with the use of a cylindrical die means.
These and other aspects of the invention are more described in the following specification and drawings.